1-Vinyl-2-pyrrolidone (hereinafter, referred to as N-VP) is used for preparing industrially useful and typically water-soluble polymer. However, it has a defect that copolymerizability with an alkyl (meth)acrylate and an alkyl (meth)acrylamide which are industrially and frequently used is low because of having a vinyl group. Consequently, when the polymerization of a material using N-VP, in particular, UV polymerization for curing in a short time is carried out, an unreacted monomer tends to be increased.
It is described in JP-A-58-152017 that in order to improve polymerizability and prepare a water-soluble polymer useful for various industries, 1-methyl-3-methylene-2-pyrrolidone (hereinafter, referred to as 1,3-MMP) having a pyrrolidone structure is used. Also, a water-containing contact lens material comprising 1,3-MMP as a main component is described in JP-B-1-15847 and JP-B-6-82177. 1,3-MMP has an amide group adjacent to a methylene group and is a compound having a similar structure as an alkyl (meth)acrylamide which is frequently used in the technical field to which the present invention belongs. Accordingly, 1,3-MMP has good solubility with the alkyl (meth)acrylamide and alkyl (meth)acrylate and is superior in copolymerizability. For example, in JP-B-6-82177, a hydrogel with high water content having a water content of 70% by weight or more in which 1,3-MMP and N-VP was copolymerized is described. It is described in these references that a hydrogel superior in flexibility is obtained by using 1,3-MMP as a main component. However, although the hydrogel with high water content is superior in flexibility, only a contact lens inferior to keep its shape is prepared. In addition, the oxygen permeability of the contact lens comprising gels with high water content which are described in these patent references is greatly lower than the oxygen permeability of water, it cannot be said that it can permeate oxygen necessary for the cornea considering the wearing state at continuous wearing or at short sleep.
On the other hand, many silicone hydrogel materials which used a hydrophobic silicone compound as a main component have been recently reported in order to improve oxygen permeability of a lens to the cornea. Further, since silicone compounds are used, the wettability of material surface is poor, and it is described in U.S. Pat. No. 5,486,579 specification in order to improve the wettability that N-VP which is a strongly hydrophilic monomer is copolymerized. However, as described above, since N-VP is low in copolymerizability with (meth)acrylate, there is high possibility that N-VP remains as an unreacted monomer in a product material when the copolymer is used as a medical device. Further, many works are required for providing a safe medical device having no residue. Consequently, in order to improve the problem, the structure of a monomer for unionizing the polymerizable group of other polymerizable components is designed in U.S. Pat. No. 5,486,579 specification for improving copolymerizability with N-VP. However, it is required to carry out the monomer design and production of all polymerizable components for using components having various functions. This is very difficult in any traders.
Further, a contact lens comprising 1,3-MMP and a silicone-containing (meth)acrylate and/or a fluoroalkyl (meth)acrylate is described in JP-A-6-214197. In the patent, the copolymerization of the silicone-containing (meth)acrylate and/or a fluoroalkyl (meth)acrylate which is used for an oxygen permeating contact lens material is described in order to improve rigidity to keep its shape and mechanical strength. However, the contact lens material being a target has a water content of about 37 to 58% and an oxygen permeation coefficient of about 26 to 35 and it cannot be said that it has adequate oxygen permeability considering the wearing state at continuous wearing or at short sleep. Further, the copolymer of the silicone-containing (meth)acrylate and/or a fluoroalkyl (meth)acrylate and a hydrophilic monomer as a main component described in JP-A-6-214197 is insufficient in the shape stability and mechanical strength.
The solubility of components composing the material is important in production of a hydrogel containing silicone. Since a material comprising a silicone-containing monomer and a strongly hydrophilic monomer tends to cause phase separation in the material, it is difficult to obtain a transparent material. An organic solvent is often used in polymerization in such a system poor in solubility. For example, a preparing method of a contact lens using 5 to 60% by weight of an organic solvent is shown in Japanese Patent No. 3249123 and a method of evaporating the solvent at a specific temperature to remove it is shown in the fore-mentioned preparing method of Japanese Patent Application National Publication (Laid-Open) No. 8-503173. However, the amount of the organic solvent used is much as several tens % in these references and when an adequate amount of organic solvent is used for obtaining a transparent material, the degree of polymerization tends to be low because of radical chain transfer to the organic solvent; therefore the lowering of the strength of a material itself cannot be evaded. Further, for the same reason, the elution amount of a monomer and an oligomer from a material is much. Further, it is troublesome and difficult to remove a large amount of the organic solvent from the system and the method is not suitable considering mass production.
The present invention was achieved considering the fore-mentioned conventional techniques and it is the purpose of the present invention to provide an ocular lens material excellent in oxygen permeability, surface wettability and the lubricity/easy lubricating property of surface, little in surface adhesive and having superior flexibility and repulsive property, and a preparing method thereof. Further, it is the purpose of the present invention to provide a safe ocular lens material by improving low polymerizability which is observed in a system using N-VP as a hydrophilic component, establishing a system in which a residual component can be reduced in production of a lens, and suppressing a monomer eluted product from the final product.